docs: def get_oath_k(args):
      """ Get the OATH K value (secret key), either from args or by prompting. """
      if args.oath_k:
          decoded = args.oath_k.decode('hex')
      else:
          t = raw_input("Enter OATH key (hex encoded) : ")
          decoded = t.decode('hex')
  
      if len(decoded) > 20:
          decoded = sha1(decoded).digest()
      decoded = decoded.ljust(20, '\0')
      return decoded